Light sources, such as light emitting diodes (LEDs) and incandescent lamps among others, suffer degradation over time. The degradation causes a decrease in the output or emitted power of the light source, which negatively impacts analog telemetry optical systems where control of the emitted power is critical in order to provide stable and accurate measurements. Optical taps can be used to split a portion of output light and send it to a detector, such that light output can be monitored and compensated.
Existing optical taps make use of several techniques, including free space optics, partial mirrors, fused fibers, and etched cladding pickoff. Producing such optical taps requires a relatively large physical device, pricey components, and expensive capital equipment, or a combination of these. An example of an early type of optical tap was made by twisting together two lengths of optical fiber, heating the twisted pair in a twist region, and pulling the twisted pair from either end to encourage fusion at the heated region. The resulting component has four ports. Typically, when monitoring transmitter power, one port is coupled to the optical source, a second port is spliced to the output fiber, a third port is redundant and so is placed in a reservoir of index-matched oil, and from the last port provides a monitored light signal from which the transmitted output power can be calculated. Such an optical tap incurs a penalty in the form of reduction of transmitted power. Some power is diverted to the monitor photodetector and some is lost by device coupling imperfections.
U.S. Pat. No. 4,475,789 teaches a fiberoptic tap used for monitoring purposes. The tap includes one fiber, having a certain mode volume, that is spliced to a second fiber having a relatively lower mode volume, such that a portion of light is radiated away from the splice, in passing from the first fiber to a second fiber. The radiated light is directed to a photodetector. The disclosed optical tap has applications in transmitter power monitoring since the radiated optical power is superfluous to the light that is capable of transmission by the line fiber. U.S. Patent Application Publication No. 2016/0025929 describes an optical tap comprising a beamsplitter, three ports, three optical fiber-supporting ferrules, and two collimating lens. The device is complex, requiring a first light beam to pass through a first port and fiber. The beam is then expanded through a collimating lens, before being split by a beam splitter. The split light is then sent to a second and third port and fiber, wherein light intensity can be monitored.
Limitations to existing optical taps include their complexity, size, and cost. In addition, to facilitate tap pickoff many of these methods impair the main light transmission path by beam splitting, resulting in a signal loss.
The present invention is directed to overcoming these and other deficiencies in the art.